Regarding a medical flexible plastic container such as infusion fluid bag, a trial of using a multilayer film as a raw material has been made to improve its properties.
Examples of a conventional medical multilayer container include those of the following polyethylene resins.
*Japanese Kokai (Laid-Open) Patent Publication No. 62-64363*
A three-layer bag of a linear low-density polyethylene, wherein each density of outer and inner layers is not less than 0.920 g/cm.sup.3 and a density of an intermediate layer is less than 0.920 g/cm.sup.3
*Japanese Patent Kokai (Laid-Open) Publication No. 63-248633*
A three-layer container of a linear low-density polyethylene, wherein each density of outer and inner layers is from 0.910 to 0.940 g/cm.sup.3, a density of an intermediate layer is from 0.880 to 0.905 g/cm.sup.3, and a difference in density between them is not less than 0.01 g/cm.sup.3
*Japanese Patent Kokai (Laid-Open) Publication No. 3-277365*
A three-layer bag comprising an outer layer of a linear low-density polyethylene having a density of not less than 0.920 g/cm.sup.3, an intermediate layer of a linear low-density polyethylene having a density of not more than 0.915 g/cm.sup.3 and an inner layer of a branched low-density polyethylene having a density of not less than 0.918 g/cm.sup.3
*Japanese Patent Kokai (Laid-Open) Publication No. 4-266759*
A bag of three or more layers, comprising inner and outer layers of a resin obtained by mixing a long-chain branched low-density polyethylene having a density of not more than 0.930 g/cm.sup.3 with 5-40% of a high-density polyethylene having a density of not less than 0.945 g/cm.sup.3, and an intermediate layer of a resin obtained by mixing a linear low-density polyethylene having a density of not more than 0.920 g/cm.sup.3 with not more than 15% of the above high-density polyethylene.
However, the above conventional medical multilayer container has any one of the following drawbacks.
(1) Since the inner and outer layers are composed with a low-density polyethylene resin, the heat resistance is not sufficient and the sealing strength and drop strength are lowered as a result of sterilization under high-temperature conditions, such as high-pressure steam sterilization, hot-water sterilization or the like. PA1 (2) After the above sterilization under high-temperature conditions, blocking is liable to arise (low blocking resistance). PA1 (3) Since the strength of the film is low, it is necessary to increase the wall thickness. PA1 (4) Since the tensile strength is not sufficient, the rate of producing bags can not be increased. PA1 (5) Since the temperature of a heater can not be increased at the time of heat sealing, sealing can not be performed in a short time (sealability is poor). PA1 (6) The transparency and flexibility are lowered after sterilization. PA1 (1) A multilayer film comprising five layers, wherein each layer is constituted by a resin having the following density in that order: PA1 (2) The multilayer film according to the above item (1), wherein the resin used in the 5th layer is a mixed resin obtained by mixing an ethylene-.alpha.-olefin copolymer having a density of 0.915 to 0.950 g/cm.sup.3 with a polypropylene having a density of 0.900 to 0.930 g/cm.sup.3 in a weight ratio of 1:3 to 9:1; PA1 (3) The multilayer film according to the above item (1), wherein the resin used in the 3rd layer is a mixed resin obtained by mixing a polypropylene having a density of 0.900 to 0.930 g/cm.sup.3 with not more than 60% by weight of an ethylene-.alpha.-olefin copolymer having a density of 0.860 to 0.930 g/cm.sup.3 ; PA1 (4) The multilayer film according to the above item (3), wherein the resin used in the 3rd layer is a mixed resin obtained by mixing a polypropylene having a density of 0.900 to 0.930 g/cm.sup.3 with 5-20% by weight of an ethylene-.alpha.-olefin copolymer having a density of 0.860 to 0.930 g/cm.sup.3 ; PA1 (5) The multilayer film according to any one of the above items (1) to (4), wherein the resin used in the 2nd layer and 4th layer is a mixed resin comprising 30-60% by weight of an ethylene-.alpha.-olefin copolymer having a density of 0.910 to 0.930 g/cm.sup.3, 35-65% by weight of an ethylene-.alpha.-olefin copolymer having a density of 0.860 to 0.900 g/cm.sup.3 and 1-10% by weight of a high-density polyethylene having a density of 0.955 to 0.970 g/cm.sup.3 ; PA1 (6) The multilayer film according to any one of the above items (1) to (5), wherein the polypropylene used in the 3rd layer has a melt flow rate of 1 to 40 g/10 min. (230.degree. C.) and a melting point of 140 to 170.degree. C.; PA1 (7) The multilayer film according to any one of the above items (1) to (6), wherein a proportion of a thickness of each layer is within the following range: PA1 (8) The multilayer film according to the above item (7), wherein the total thickness of the film is from 200 to 300 .mu.m; PA1 (9) A container which is obtained by molding the multilayer film of any one of the above items (1) to (8), said container comprising the 1st layer of this multilayer film as an outer layer and the 5th layer as an inner layer; and PA1 (10) The container according to the above item (9), which is obtained by interposing a polyethylene port member between the films and welding the port member with the films.
When a medical container (infusion fluid bag) 10 as shown in FIG. 1 is produced, two films 22, 22 are piled up each other and peripheries of films 22, 22 are heat sealed in the state where a port member (port) 20 it inserted between the films.
However, as shown in FIG. 2, since the film 22 bends largely at the portion adjacent to the port member 20, when a conventional multilayer film is heat-sealed, the film is stretched at the bending portion 24 and the film thickness is reduced. Therefore, pinhole is liable to arise.